solar energy

...either into thermal energy (heat) or into electrical energy, though the former is easier to accomplish. Two main types of devices are used to capture solar energy and convert it to thermal energy:
flat-plate collectors and concentrating collectors. Because the intensity of solar radiation at the Earth’s surface is so low, both types of collectors must be large in area. Even in sunny parts of...

solar heating

...less commonly air) that is then pumped to a conversion, storage, and distribution system. In liquid-based systems, water (or less commonly glycol) is pumped through tubes that are in contact with a
flat-plate collector. The latter is a blackened metal plate that absorbs sunlight and is insulated on the front with layers of glass and air; the glass allows visible light to fall on the plate but...